It is well-known to inspect cigarettes prior to packaging for purposes of detecting if there is an inadequate loose charge of tobacco near the end or if a cigarette in a bundle is broken or if it is a "short-stick" (improper length). Such an inspection is highly desirable from the standpoint that a consumer is annoyed and risks injury if the cigarette is improperly filled. Inspection is also necessary to determine that the consumer receives value for his money and does not receive a short or broken cigarette.
It is therefore desirable to reject cigarettes which do not meet proper specifications so as to maintain high speed production while at the same time providing customer satisfaction.
One known technique for detecting missing and improperly filled cigarettes is mechanical inspection. Mechanical inspection employs pins which are pushed against the end portion of cigarettes. The extent to which a pin penetrates indicates the amount of tobacco shreds in the end portion of a cigarette. However, mechanical inspection is undesirable because of speed limitations. Further, it is very difficult to mechanically inspect whether or not a cigarette in a bundle is broken and to provide inspection techniques to determine if cigarettes are of incorrect length.
Optical techniques are known for detecting missing and improperly filled cigarettes. See, for example, U.S. Pat. Nos. 4,266,674 and 3,980,567. In these types of systems a light producing source illuminates the end portions of a bundle of cigarettes and a transducer is used for sensing reflected light from the end portions to determine whether or not the end portions are properly filled with tobacco. However, in prior art inspection systems they have been found subject to inaccuracies.
U.S. Pat. No. 4,266,674 discloses a photodetector apparatus used to detect missing and improperly filled cigarettes. However,its speed is limited due to its sequential circuitry.